The assessment of single and double vision (diplopia) are important in a variety of conditions which affect the alignment of the eyes and extraocular muscle function. This information can be used to detect and quantitate the degree of double vision, for example, and thus has both diagnostic and therapeutic applications.
Current methods for assessing double vision involve the use of devices originally developed to assess conditions other than double vision. One group of tests includes the tangent and Hess screen tests. These tests use a flat test area without a means for verifying eye position at the time double vision is reported. Another related test, known as the Goldmann test, uses a visual field testing device with test lights disposed in a large white bowl.
Other approaches currently used to estimate diplopia involve measuring displacement of corneal light relative to known landmarks in the front of the eye. Such tests provide only minimal quantitative information and can vary significantly based on measurements obtained by different examiners. More recently, equipment for detecting head alignment in patients with spinal cord disorders has been adapted to estimate diplopia. These methods offers precise quantification but include significant shortcomings such as high cost, large and unwieldy equipment, and an availability, which is typically limited to only subspecialists.
One significant drawback to existing methods for assessing diplopia is that eye position cannot be correlated to a patient's report of double vision. This is important since the brain can suppress input from one eye in order to avoid diplopia. Additionally, significant deviations of the eye muscles can be missed without viewing the patient's eyes from the front during examination. A need therefore exists for a simple, accurate, and quantitative means for assessing eye diseases.